1. Technical Field
The present invention relates to a discharge lamp driving device, a light source, a projector, and a discharge lamp driving method.
2. Related Art
Recently, energy savings are desired in projectors. Therefore, projectors equipped with various lighting modes are provided, such as a low-power mode in which drive power to the lamp is lower than usual, a dimming mode in which drive power is changed synchronously with video signals, and a standby mode in which drive power is lowered when video signals are not inputted from outside. For example, in the low-power mode, since lower drive power is supplied to the lamp, the load on the electrodes is lower, thus increasing the service life of the lamp.
However, if drive power is lower than rated power, the protrusions at the distal ends of the electrodes cannot be melted sufficiently. As the lighting is continued for a longtime, the protrusions get worn and reduced. The reduction of the protrusions means the expansion of the distance between the electrodes, causing a fall in illuminance. That is, if the shape of the protrusions at the distal ends of the electrodes cannot be maintained, the advantages of the low-power mode cannot be achieved and a problem of shorter service life of the lamp arises. Thus, in order to overcome this problem, a discharge lamp lighting device and a projector in which the lamp is driven in a refresh lighting mode to promote the melting of the protrusions of the electrodes during a predetermined period after the lighting of the lamp are proposed (see JP-A-2008-270058).
In the projector of JP-A-2008-270058, lamp power above the rated power value is supplied in the refresh lighting mode. In this case, it is anticipated that the protrusions formed in normal lighting are melted excessively and cannot be maintained in shape. Consequently, the lamp flickers as the lamp cannot maintain stable discharge. Also, a high load is on the arc tube and may cause inconvenience such as crystallization of the quartz glass or so-called, denitrification.